In an air conditioning (A/C) system, such as used in a vehicle, a compressor is typically used to compress a gaseous refrigerant. In a vehicle, the compressor is usually operated from the vehicle engine by a fan belt through an electrically controlled clutch. A lubricant is provided in the system which ideally is uniformly mixed in the refrigerant and flows around the system with the refrigerant to lubricate all the system components, including the compressor.
However, when the system has not been used for a period of time, for example over a day or longer, refrigerant in liquid form can pool in low areas in the system. Further, the lubricant can separate out of the refrigerant and pool in the low areas as well. On the next occasion that the compressor is operated, it must purge the liquid refrigerant and lubricant, which generates noise and places stress in the components of the compressor. This is sometimes referred to as liquid slugging. The presence of slugs of liquid can cause vibration, noise, clutch failure, and/or damage to the compressor because the collected liquid cannot be compressed.
Attempts have been made to address this problem by intermittently starting the compressor to purge the liquid by controlling the clutch operation. For example, Japanese Patent Application Publication 55-012277A of Jan. 28, 1980 discloses a starting controller for a compressor, such as used in a vehicle, which causes the magnetic clutch driving the compressor to be intermittently engaged to discharge liquids from the compressor before beginning continuous operation after a predetermined lapse of time. The document discloses two on/off cycles before beginning continuous operation. The document suggests operation of the clutch for approximately 1/50 to 1/10 second intervals, as an example. Japanese Unexamined Utility Model Application 58-116964 of Aug. 10, 1983 discloses a control device for a vehicle air conditioner that performs on/off control of an electromagnetic clutch for three on/off cycles before beginning continuous operation. U.S. Pat. No. 7,836,715 issued Nov. 23, 2010 to Eisenhour discloses a similar device.
However, a need exists to provide an enhanced mechanism to reduce the wear and noise generated by this slugging condition.